Process for de-icing an air intake cowling of a reaction motor and device for practicing the same

ABSTRACT

The object of the invention relates to a process for de-icing an air intake cowling ( 5 ) of a reaction motor, comprising an air intake lip ( 6   a ), a de-icing system ( 10 ) and acoustic attenuation means ( 11 ), characterized in that it consists in constituting said acoustic attenuation means by separate islands ( 11   a ) each formed by a sandwich comprising an acoustically resistive porous layer forming a portion of the external envelope ( 6   i ) of the fan channel delimited by said air intake lip, a cellular core, and a reflector ( 13 ), in sending into said lip, preferably in the direction of said acoustic attenuation islands, the warm fluid under pressure of said de-icing system, and causing said fluid to escape outside said cowling, through one or several openings ( 20 ) of suitable shape and size, provided in said cowling.

[0001] The present invention relates to de-icing air intake cowlings ofreaction motors, particularly aircraft.

[0002] The requirements of the authorities for certification and therules concerning noise imposed by airports limit the level of noiseneeded during takeoff and landing. The noise generated by a transportairplane arises both from the airframe and from the motor. The noise ofthe motor originates in different sources, such as for example the noisegenerated by the turbine or by the compressor or the noise generated bythe fan.

[0003] The noise produced by the motor is preponderant over the noisegenerated by the airframe in the takeoff phase because the motoroperates in full throttle.

[0004] This source of noise is detrimental. For example, above a certainvalue, the aircraft will not be permitted to take off or to land otherthan at certain specified times that are not troublesome for the localcommunities.

[0005] This is the reason why certain precautions are nowadays taken byaircraft builders and engine makers to decrease the sonic emissions ofthe motors installed in aircraft.

[0006] Thus, panels for the attenuation of noise engendered by aircraftmotors are installed in certain places in the nacelle, for example atthe intake and outlet of the fan channel, or else on the doors of thepressure reversers.

[0007] From FR 2 261 583, there is known an acoustical treatment for anair intake of an aircraft motor in which the acoustic panel is appliedsymmetrically to the fan channel for optimum suppression of noise.

[0008] In EP 0 823 547, so as to improve further the acousticattenuation, there are added acoustic attenuation panels to the attackedges of the air intake lip of the cowling.

[0009] Nevertheless, these attack edges are subjected to temperature andmoisture conditions such that at present ice forms on them. Theformation and accumulation of ice on the attack edge of the air intakelip poses several problems. If large pieces of ice break off, they thuspenetrate the air intake and are ingested by the motor, thereby riskingdamaging the elements of said motor and decreasing performance.Moreover, the accumulation of ice modifies the contours of the attackedge of the air intake lip and generates undesirable aerodynamiceffects.

[0010] To solve these problems, de-icing systems for the air intake edgehave been installed. They inject warm air under pressure, taken from themotor, directly onto the skin of the internal surface of the air intakelip to prevent in the most effective manner possible the formation andaccumulation of ice under conditions of normal use of the motor.

[0011] However, in EP 0 823 547, panels constituted of a sandwichcomprising a honeycomb structure bounded, on the air flow side, by anacoustically resistive layer and, on the opposite side, a rearreflector, are added to the interior of the attack edges of the airinlet lip.

[0012] These acoustic attenuation panels added to the attack edge of thelip form a screen and preventing warm air under pressure to reheat theattack edge of said lip and to melt the ice which is accumulatedthereon. Carrying out commercial flights can, under certain climaticconditions, be dangerous.

[0013] Thus, the conventional de-icing system with the injection of warmair under pressure cannot be used in the context of acoustic treatmentsuch as described in EP 0 823 547.

[0014] Moreover, U.S. Pat. No. 5,841,079 discloses an acousticattenuation panel located in the air inlet lip and permitting de-icingsaid lip. The air inlet comprises a lip comprising an acoustic panel anda device for the injection of fluid under pressure, said fluid having atemperature sufficient to avoid the formation of ice on the air inletlip. The acoustic panel is conventionally: a honeycomb core sandwichedbetween a porous layer and an acoustical reflecting layer. The porouslayer and the acoustically reflecting layer are both pierced with holesso as to permit the fluid under pressure to pass through the acousticpanel and de-ice the lip.

[0015] However, the geometry and dimensions of the air inlet are adaptedto the performance of the motor. The latter thus “seize” an airflow ratecorresponding to the inlet air.

[0016] Nevertheless, the device described in U.S. Pat. No. 5,841,079increases, because of said holes, the air flow ingested by the motor.The motor can thus be facing different airflow rates accordingly as thede-icing system is activated or not. This has a certain effect on itsperformance, runs counter to the wishes of engine builders who definethe performance of their engines relative to a fixed air intakegeometry.

[0017] Moreover, the confrontation in the cells of the honeycomb, of thesonic waves with the fluid under pressure, disturbs the operation of theacoustic panel, which decreases the acoustic efficiency of said panel.

[0018] The invention seeks to overcome the drawbacks and limitations ofthe existing systems set forth above, by providing a solution permittingassociating the conventional de-icing system with the injection of warmair under pressure, and the addition in the attack edge of the air inletlip of an acoustic attenuation panel.

[0019] To this end, the invention has for its object a process forde-icing an air intake cowling of a reaction motor, comprising an airinlet lip, a system for de-icing the lip supplied with warm fluid underpressure, and means for acoustic attenuation forming an integral portionof a predetermined region of said lip, characterized in that it consistsin constituting said acoustic attenuation means by separate islands eachformed by a sandwich comprising an acoustically resistive porous layerforming a portion of the external envelope of the fan channel delimitedby said air intake lip, a single or multi-layer porous cellular core,and a reflector, sending into the lip, preferably in the direction ofsaid acoustical attenuation islands, the warm fluid under pressure ofsaid de-icing system, and causing said fluid to escape outside saidcowling, through one or several openings of suitable shape and size,provided in said cowling.

[0020] The acoustic function is carried out by the islands whose poroussurface is exposed to the aerodynamic flow and permits attenuating thenoise generated by the motor.

[0021] The de-icing function of the air intake lip, particularly in linewith the blower channel, where the acoustic attenuation structure islocated, is efficaciously produced by the flow of warm fluid whichenters into the spaces between the islands, preferably arranged todefine between them corridors or throats more or less straight orsinuous and suitably oriented, so as to bathe directly the internalsurface, not covered by the islands, of the wall of the lip.

[0022] Effective de-icing is thus ensured at the height of the internalwall of the lip and without the rejection of de-icing fluid into the fanchannel because where the fluid bathes said wall, there is nocommunication with the outside of the lip, the wall of this latter atthis place not being porous.

[0023] Increased de-icing is moreover performed by said porous surfacesof the islands, which bathe in the warm fluid, by conduction or throughthe cellular structure.

[0024] The islands can have different structures and be constituted byjuxtaposed strips of a honeycomb material or of juxtaposed tubular lugsperpendicular to the wall of the air intake lip.

[0025] As a modification, the islands can have a common reflectorcovering all of them and provided with scoops channeling the de-icingair toward the inter-island spaces.

[0026] The invention also has for its object the air intake cowlingsobtained by the practice of the process described above, particularlythose which will be described hereafter by way of example forillustration of the process, and with respect to the accompanyingdrawings, in which:

[0027]FIG. 1 is a schematic perspective view of an aircraft reactionmotor;

[0028]FIG. 2 is an axial cross-sectional view of the air intakestructure of the motor of FIG. 1;

[0029]FIG. 3a is a perspective view of a section of the air intake lipof FIG. 1 provided with an acoustical attenuation structure withde-icing function, according to the invention;

[0030]FIG. 3b is a fragmentary cross-sectional view of an air intake lipof the type of FIG. 3a;

[0031]FIGS. 4a and 4 b show two modified embodiments of an acousticalattenuation structure according to the invention using a honeycombmaterial;

[0032]FIGS. 5a and 5 b show two embodiments of an acoustical attenuationstructure according to the invention using tubular lugs;

[0033]FIGS. 6a and 6 b show two modified embodiments of an air intakelip according to FIG. 3b;

[0034]FIG. 7 is a front cross-sectional view of a lip, perpendicular tothe axis of the fan channel, showing a modified embodiment of astructure combining de-icing and acoustical attenuation, according tothe invention;

[0035]FIG. 8 is a perspective and cross-sectional view on the lineVIII-VIII of the structure of FIG. 7, and

[0036]FIG. 9 shows a modification of the device of FIG. 8.

[0037] There is shown in FIG. 1 an aircraft turbo reactor comprising anacelle 1 coaxially surrounding the motor itself and fixed for exampleto a wing (not shown) of the aircraft by means of a mast generallydesignated by reference numeral 2.

[0038] The nacelle 1 has an annular cross-section and defines betweenitself and the central portion of the motor, an annular channel 3 calleda fan channel. There is shown at 4 in the drawing, the nose of ogiveshape of the fan driven by the motor and which is disposed at the inletof the channel.

[0039] The front portion of the nacelle defines an air intake cowling 5which has for its function to ensure the aerodynamic flow of the air, onthe one hand, toward the fan channel 3 and, on the other hand, towardthe exterior of the nacelle 1.

[0040] As can be seen in FIG. 2, which is in fragmentary axialcross-section of the cowling 5, the latter is prolonged forwardly by anair intake lip 6 having a U-shaped cross-section opening rearwardly.This lip ensures the division of the air between the portion 7 whichenters the fan channel and the portion which flows about the nacelle.

[0041] The rear of the lip 6 is formed by an internal partition 8.

[0042] As shown schematically in FIG. 2, the invention seeks to combinede-icing of the lip 6, in particular its wall delimiting the inlet ofthe fan channel 3, with the help of a conventional system using warm airunder pressure delivered into the annular space delimited by the lip,and an acoustical attenuation about the internal periphery of the lip.The de-icing system is for example constituted by an annular tubingindicated at 10, provided with a plurality of ejection orifices orequivalent system, also known and formed by injectors with one orseveral injection nozzles.

[0043] According to the invention, particularly the wall of the lip 6turned toward the fan channel 3, is provided with an acousticalattenuation structure of the sandwich type constituted by a cellularcore or the like, covered, on the one side, with an acousticallyresistive porous layer and, on the other side, with a total reflector,said structure being symbolized at 11 in FIG. 2 and extending preferablycircularly over all the internal periphery of the lip.

[0044] The lip 6 is generally constituted by four sections or sectors of90°, as shown in FIG. 1, abuttingly joined with fasteners.

[0045]FIG. 3a shows a perspective of one of these sectors, 6 a, providedwith an acoustic attenuation structure 11 according to a firstembodiment.

[0046] The acoustic attenuation structure 11 is constituted by islandsin the form of strips 11 a disposed in parallel, with a predeterminedspacing between them, in an annular region of the lip (6 a) coaxial withthe fan channel 3, and extending from one end to the other of the sector6 a.

[0047] In the embodiment shown in FIG. 3a, each island strip 11 a foracoustical attenuation is connected and fixed, with the help of suitablemeans of which examples will be given later, onto the internal surfaceof the internal wall 6 i of the lip, in a region in the form of a stripof a predetermined width.

[0048] Each island strip 11 a comprises a central cellular core 12 ofthe honeycomb type, the axes of the cells being perpendicular to thewall 6 i of the lip.

[0049] The recesses 12 are closed, on the internal side of the lip, by alayer or skin 13 forming a total reflector and, on the other side, by aportion 14 of the wall 6 i which is rendered porous for example bypiercing holes represented by 15 on the enlarged portion of FIG. 3a, thereference 15 indicating on the other portion of the figure simply theemplacement of each group of holes of each cell 12.

[0050] Between the portions 14 of the wall 6 i of the lip, extendportions 16 corresponding to the intervals between strips 11 a and whichare not pierced.

[0051] The region of the wall 6 i of the lip facing the acousticattenuation structure 11 extends for example between the tubing 10 forthe supply of warm air under pressure for de-icing, and the internalpartition 8.

[0052] The strips 11 a are preferably disposed obliquely such that thespaces between strips form corridors or throats whose direction (arrow17) is not perpendicular to the partition 8.

[0053] In other words, the axis 17 of the strips 11 a forms an anglerelative to the axis of the fan channel 3, symbolized by the arrow 18 inFIG. 3a. Such an orientation of the strips gives better mixing of theflow circulating within the lip and a better quality of heat exchange.

[0054] The tubing 10 is pierced in known manner with openings 19, ifdesired provided with injection nozzles, distributed along the tubingand oriented toward the regions to be de-iced.

[0055] These openings 19 direct de-icing air particularly toward thecorridors between the strips 11 a which channel it by forcing it tobathe the internal surface of the portions 16 of the wall 6 i of thelip.

[0056] The air then escapes to the external atmosphere in theconventional way, which is to say by means of one or several openings,for example in the form of slots whose number and size as well as theirdistribution over the external periphery of the cowling 5 can vary.

[0057] There is shown in FIG. 3a, at 20, such an opening for a rejectionto the exterior of the lip.

[0058] In FIG. 3b, which is a schematic transverse cross-section of anair intake lip 6 of the type of FIG. 3a, there is shown in cross-sectionthree strips 11 a disposed obliquely and covering a region of width 1 ofthe wall 6 i between the tubing 10 and the partition 8.

[0059] This region can be enlarged up to the extreme front end of thelip 6 to achieve a width 1′ so as to improve acoustic attenuationwithout thereby degrading de-icing.

[0060] There is shown schematically at 20 in FIG. 3b, an openingprovided in the external wall 6 e of the lip to reject to the exteriorof this latter, opposite the fan channel 3, the de-icing air.

[0061] At 21 is schematically shown a modification of an openingprovided more downstream in the cowling 5 to reject de-icing air comingfrom the interior of the lip 6 via a conduit 22 passing through thepartition 8.

[0062] In the devices shown in FIGS. 3a and 3 b, not only is an acousticattenuation function performed by the attenuation strips 11 a, butsuitable de-icing of the internal wall 6 i of the lip is also ensured,both directly in the portions 16, and indirectly in the portions 14, byconduction through the cellular structure 12.

[0063] This de-icing is ensured without rejecting air into the fanchannel 3, because the air does not reach the portions 14 and isrejected externally of the cowling 5.

[0064] The dimensions of the cells of the structures 12, particularlythe height, may of course vary.

[0065] The structures 12 are single layer or multi-layer, which is tosay with superposed resonators, separated or not by septa.

[0066] As a function of the conductibility of the materials used, theintervals between the strips 11 a are suitable to the quality of desiredde-icing.

[0067]FIGS. 4a and 4 b show modified embodiments in which the strips ofislands have a different width, two rows of cells in the strips 11 b ofFIG. 4a, three rows in the strips 11 c of FIG. 4b.

[0068] The interval between strips is relatively great in FIG. 4a orrelatively small in FIG. 4b in which the path of the de-icing air in thethroats zigzags as indicated by the arrow.

[0069] Instead of annular tubing 10 extending through all the lip 6, thede-icing system can be constituted, also in known manner, by one orseveral injectors, emptying into the lip 6 at one or several places andeach comprising one or several injection nozzles directing warm air in acircular path within the lip, the air escaping outwardly as in the caseof tubing 10. Such a system is shown schematically in FIGS. 7 and 8,which will be described later.

[0070] In this case, the orientation of the strips 11 a is such as totake account of the direction of circulation of the de-icing air withinthe lip 6.

[0071]FIGS. 5a and 5 b show two embodiments of the acoustic attenuationstructure 11 in the form of islands 23 constituted by tubular lugsseparated from each other or together, according to all possiblecombinations.

[0072] The island lugs 23 are for example simple cylindrical tubes ofcompatible material as to welding or braising to the lip 6. The tubesare closed at one end by a layer or skin 23′ forming a reflectoranalogous to the reflector 13 of the island strips 11 a. They areconnected and fixed to the internal surface of the wall 6 i of the lipat the desired positions, then the portion of the wall 6 i facing thetubes is pierced like the portions 14 a of FIG. 3a.

[0073] These island lugs 23, which contain for example simply air,thereby ensure the acoustic attenuation function. The lugs 23 can ofcourse, like the strips 11 a, constitute superposed resonators separatedby septa.

[0074] In a manner analogous to that described with respect to theisland lugs 11 a, the de-icing air will flow between the lugs 23, asshown by the arrows in the figures between the individual lugs (FIG. 5a)or between the rows of lugs (FIG. 5b) which are for example orientedlike the strips 11 a of FIG. 3a.

[0075] Acoustic attenuation is ensured in line with the lugs 23 and thede-icing in line with the intervals between the lugs, as well as in asupplemental way by conduction in line with the lugs.

[0076]FIGS. 6a, 6 b show two other modes of construction of the portionof the wall 6 i of the lip where the two functions of de-icing andacoustical attenuation take place.

[0077] Although in the case of FIG. 3b, the lip 6 is made first in itstotality and then pierced at the desired positions, in the embodiment ofFIG. 6a, the lip 6′ is made partially, which is to say without theportion (6′a) of the internal wall 6 i integrating the acousticattenuation structure.

[0078] This portion 6′a is produced separately and can be constituted ofthe same elements as those of FIG. 3b except that the wall 24 to whichis secured the elements 12 and 13 analogous to those of FIG. 3b, have anannular shape and are secured and fixed, on the one hand, to itsupstream edge, on the wall 6 i at 25 and, on the other hand, to thedownstream wall, on the partition 8 at 26.

[0079] The holes 15 in the wall 24, facing the acoustic attenuationisland strips 11 a, are pierced before emplacement on the portion 6′a.

[0080] In FIG. 6b, the lip 6″ is identical to that of FIG. 3b and theacoustic attenuation structure is formed by a complete panel, which isto say the island strips 11 a each comprising a cellular central core12, a reflector 13 on the internal side of the lip 6 and a layer 27 forexample of a sheet of aluminum on the side of internal wall 6″i of thelip.

[0081] The assembly is connected and fixed by welding or cementing at 28and 29 against said wall 6″i which is then, as well as the sheet 27,pierced with holes 15 facing said strips 11 a.

[0082] In the various embodiments described above, the extent of theregion to be perforated of the internal wall (6 i, 6′i, 6″i) of the lip,as well as the size and distribution of the holes 15 in the lip, aredetermined by a computer, in a known manner, as a function of thedifferent parameters connected to the frequencies characteristic of thenoise to be attenuated, to the type of motor, to the nacelle, to thematerials used, as well as to the conditions of operation and use of themotor and of the aircraft. The object that is sought is to obtain thebest ratio between acoustic gain and loss of de-iced surface.

[0083] The cellular structure 12 with its reflective layer 13, which isto say the strips 11 a, are secured on the internal surface of the lip,directly or indirectly by means of a metallic sheet 27, by braising,welding or cementing with the help of an adhesive according to thenature of said strips 11 a and the wall of the lip. The cellularstructure is preferably metallic, for example of stainless steel or ofaluminum.

[0084]FIG. 7 is a front view in cross-section of a lip 6′″ constitutedof four sectors of 90° held together in abutment by fasteningsschematically shown at 30.

[0085] The acoustic attenuation structure 11′ is, according to amodification shown in perspective and in fragmentary view in FIG. 8,constituted of parallel strips 11′a separated by two corridors 31 andeach comprising a central cellular core, a reflector 13′, and a porouswall delimited by a portion of the internal wall of the lip 6′″, piercedwith holes 15.

[0086] The strips 11′a are, in this modification, orthogonal to the axisof the fan channel 3, which is to say parallel to the partition 8.

[0087] Moreover, the reflector 13′ is common to the trips 11′a and alsocovers the corridors 31 separating the strips 11′a, although saidreflector 13′ is provided in line with each corridor 31 and along thislatter, with scoops 32 aligned and oriented in the direction ofcirculation of the de-icing air. This air is, in the present case,introduced into the lip 6′″ with the help of one or several injectionsystems such as that symbolized at 1 in FIGS. 7 and 8, whose nozzle ornozzles B is or are directed tangentially to the lip so as to give tothe air a circular trajectory (arrow A). The air introduced into thecorridors 31 by means of the scoops 32, as shown by the arrows 33 inFIG. 7, leaves at the end of the section of the structure 11′, as shownby the arrow 34, adjacent one of the fastenings 30.

[0088] The de-icing air is rejected outside the air intake cowling as inthe case of FIG. 3b, directly from the lip 6′″, by one or severalopenings or slots such as 20, or indirectly through one or severalopenings or slots such as 21.

[0089] The acoustic attenuation structures 11′a can of course beconstituted by tubular lugs, such as the lugs 23 of FIGS. 5a, 5 bcovered with a common skin, forming a reflector and provided with scoopsfacing the spaces between the lugs.

[0090] The dimensions of the portions forming resonators, their mutualarrangement and the degree of porosity of the porous portions integratedinto the internal wall of the lip 6′″, can also vary over broad ranges,as in the various preceding embodiments.

[0091]FIG. 9 shows a modified embodiment of FIG. 8 according to whichthe strips 11″a are individual, which is to say each provided with areflector 13″, the corridors 31 between the strips not being covered aswas the case in FIG. 8.

[0092] On the contrary, the ensemble of said strips 11″a is covered witha slightly bowed piece 40 fixed on the lateral edges of the set ofstrips, from one end to the other.

[0093] Moreover, one or several openings are provided in the piece 40 topermit air (A) introduced into the lip by the nozzle or nozzles B, topenetrate below the piece 40 which channels the air toward the corridors31, the air leaving at the end of these latter being then evacuatedoutside the lip as in the preceding embodiments.

[0094] The embodiments of FIGS. 7, 8 and 9 can be used by constructing,as in the device of FIG. 6a, the lip in two portions of which onecontains the acoustic attenuation structure (11′) and is connected tothe other to define the complete lip.

[0095] It is finally to be noted that the strips such as 11 a and thealignments such as 23, in FIG. 5b, can be provided with transversegrooves, passages or corridors so as further to improve heat exchange.

1. Process for de-icing an air intake cowling (5) of a reaction motor,comprising an air intake lip (6, 6′, 6″, 6′″), a system (10, 1) forde-icing the lip provided with warm fluid under pressure, and acousticattenuation means (11, 11′) forming an integral portion of apredetermined region of said lip, characterized in that it consists inconstituting said acoustic attenuation means by separate islands (11 a,11′a, 11 b, 11 c, 23) each formed of a sandwich comprising anacoustically resistive porous layer forming a portion of the externalenvelope (6 i) of the fan channel (3) delimited by said air intake lip,a single or multi-layer porous core, and a reflector (13, 13′), insending into the lip, preferably in the direction of said acousticattenuation islands, the warm fluid under pressure of said de-icingsystem, and causing said fluid to escape outside said cowling, throughone or several openings (20, 21) of suitable shape and size, provided insaid cowling (5).
 2. De-icing device for an air intake cowling obtainedaccording to the process of claim 1, said cowling (5) comprising an airintake lip (6, 6′, 6″, 6′″), means (10, 1) for the injection into thelip of a warm de-icing fluid under pressure, acoustic attenuation means(11, 11′) forming an integral portion of a predetermined region of saidlip, and means (20 to 22) for evacuating outside the cowling thede-icing fluid, characterized in that said acoustic attenuation meansare constituted by separate islands (11 a, 23) each formed of a sandwichcomprising an acoustically resistive porous layer (14) forming a portionof at least the internal wall (6 i, 6′i, 6″i) of the lip, a centralcellular core (12) and a reflector (13, 13′, 23′).
 3. De-icing deviceaccording to claim 2, characterized in that the central core (12) of theislands is a honeycomb structure.
 4. De-icing device according to claim3, characterized in that the central core of the islands is formed oftubular lugs (23).
 5. De-icing device according to claims 2 and 3,characterized in that the separate lugs are strips (11 a, 11 b, 11 c)formed of at least one row of cells, disposed in parallel.
 6. De-icingdevice according to claims 2 and 4, characterized in that the separateislands are alignments of juxtaposed tubular lugs (23) disposed inparallel.
 7. De-icing device according to one of claims 2 to 6,characterized in that the reflector (13′) of the islands is in commonand provided with scoops (32) communicating with the spaces (31) betweenislands, bordered by the non-porous portions of the wall of the lip(6′″).
 8. De-icing device according to one of claims 2 to 6,characterized in that the assembly of the islands (11″a) is covered witha piece (40) channeling the de-icing fluid toward the spaces (31)between islands.
 9. De-icing device according to one of claims 2 to 6,characterized in that said strips (11 a) or alignments (23) are obliquerelative to the axis of the fan channel (3).
 10. De-icing deviceaccording to claim 9, characterized in that the de-icing fluid isdistributed in the lip (6, 6′, 6″) by circular tubing (10) provided withejection openings (19) suitably oriented.
 11. De-icing device accordingto one of claims 2 to 8, characterized in that said strips (11′a) oralignments are orthogonal to the axis of the fan channel (3). 12.De-icing device according to one of claims 7, 8 and 11, characterized inthat the de-icing fluid is distributed in the lip (6′″) by one orseveral ejection devices (1) creating a circular flow (A) of the fluidin the lip.
 13. De-icing device according to one of claims 2 to 12,characterized in that the lip (6′) is formed from two assembled portionsof which one (6′a) integrates the acoustic attenuation structure (11 a).